In the production of materials such as high quality silicone sealant base, a one component thixotropic material having a viscosity up to 1,000,000 centipoises, it is conventional to use a tubular or basket type filter system. These filters help to assure the smoothness and the uniformity of the silicone material. In filter designs of the prior art, the acceptable pressure drop across filter screens has been limited to under 240 pounds due to limitations of the filter design. Furthermore, the open passages are a minor part, generally less than 8% of the surface of the filter because of the structural material arrangement.
The prior art filters are also generally designed to pass fluids from the outside to the inside of the filter basket assembly and then upwardly through the outlet of the filter. A typical design would comprise a high pressure wire wound spiral of approximately 0.050 square spaced 0.002 inches to 0.006 inches apart with reinforcement every 3/8 inches on the inside. This design would permit a mass of 0.002-0.006 inches by 3/8 inches wide to pass through the filter, resulting in a rather poor filtration.
The present invention comprises an improved filter which includes a filter basket assembly wherein the fluid flow is from the inside to the outside of the assembly in contrast to the prior art. Under inside to outside flow conditions a filter screen can endure greater stress than it would under outside to inside flow conditions. This is due to what is known as "hoop stress phenomenom," i.e., that a hoop configuration can sustain under tension forces that would cause failure under compression. The filtering element comprises a flat elongated screen rolled on its shorter dimension and inserted into a perforated tube. A top handle assembly and a base are coupled to the perforated tube at the respective ends thereof by means of an elongated rod which extends longitudinally within the tube in order to hold the assembly together.
The filter assembly has the advantage of a substantially greater passage surface area than known filters, having open passages that are as much as 60% of the filter surface. It also limits the particle passage to a size equal to the mesh openings, thereby insuring smoothness and uniformity of the product. Furthermore, the filter is suitable for applications where the pressure drop across the filter screen ranges up to about 1,000 p.s.i., and it has the additional advantage of using a filter screen that is simple and inexpensive to manufacture and is readily replaceable or reusable over a period of time.